For my second Circuit Notes entry I decided to go with the Wien Bridge Oscillator. This time around the math wasn’t as intensive as it was for the Type III compensation with one exception. I had originally got the right answer in my derivation but had made a math error in the final step that I caught while writing in my Field Notes book. When I corrected the mistake I no longer knew how to make the math work out to give the correct output voltage at the resonant frequency. Wikipedia helped some by claiming RC was normalized to 1 but didn’t state why and I still don’t know. Is it just to make the math easier or is there a deeper reason for doing so?
Maybe college me could figure it out but present me is a tad rusty and so that last step is left as an exercise to the readers. I’ll keep digging and post an update if I find it or someone can correct me. Either way, the Evernote link can be found here and if you have any recommendations for a circuit you’d like to see analyzed feel free to send them my way.
The other week I impulse bought a bunch of Field Notes notebooks under the justification that they were a birthday gift to myself. I’ve been carrying a small pocket notebook on me for at least a year now so the regulator sized Field Notes won’t be stuffed in a drawer somewhere and forgotten but I also broke down and ordered a pack of the new limited release Arts & Sciences books too and needed a good use for them. They’re beautiful notebooks and I definitely recommend picking up a pack or two while you still can.
After brainstorming a bit I got the idea of using them to compose a circuit reference for myself. I seem to find my self deriving the same formulas over and over again at work so putting them all in one place where I can easily look back on them made the most sense. In order to keep this site from stagnating I figured I may as well also share them with whoever wants them. The Arts and Sciences books are the perfect size (7.5″ x 4.5″) and layout to fit a schematic on the blank left page and the derivation with some notes on the grid/lined right page. As an added bonus, writing out the circuits by hand with the idea of needing the info later will, ideally, help me to improve my normally atrocious penmanship as I have to take my time and focus on my writing.
Without further ado, here’s the Table of Contents and first entry into what I’m calling my Circuit Notes Series. I went with the transfer function for Type III compensation for switching regulators. Checkout the cool reference tables Field Notes threw on the inside cover too. Since this is just a reference I didn’t include all the math or in-depth details of how the circuit works, just some key notes to keep in mind. Think of this as an introduction to the circuit, not a be all end all treatise.
For anyone who would like to save a digital copy of these derivations I’ve also posted these pages to Evernote (here and here) where you can add them to your own notebooks and search them using OCR. Hopefully someone finds these notes as useful as I do! The next note I do will be on an RC oscillator circuit and after that who knows? Recommendations for circuits are welcome too as I’m always willing to learn some new topology.